Known engine carburetors contain an idling circuit which operates at starting and during idle speed of the engine, but is not needed during normal driving conditions. There are situations during normal driving conditions, however, when high vacuum pressure in the manifold drastically increases fuel consumption from the idling circuit even though the engine does not require extra power. Such situations include deceleration from high speed, driving on a downward slope, shifting gears, applying the brake, or releasing the accelerator pedal. In these cases, fuel is wasted and additional air pollution results.
It would therefore be advantageous to disable the idling circuit when the engine is running at speeds in excess of idle. If this is accomplished, fuel can be conserved, and air pollution minimized.